1. Field of the Invention
The present invention relates generally to key switch units. The present invention relates more particularly to a key switch unit compatible with smaller, thinner keycaps.
2. Description of the Related Art
In notebook personal computers, keycaps provided in keyboards are becoming increasingly small and thin as the computers are reduced in size and thickness. The keycaps of keyboards, which are resin molded products, vary in vertical or horizontal size or shape depending on their types. For example, keycaps used for a Spacebar, a Shift key, an Enter key, etc., have a horizontally elongated shape larger in horizontal (right-left) dimension than other keycaps such as those of alphanumeric keys.
Such keycaps horizontally elongated in shape are low in strength where the thickness is reduced because of thinning. Therefore, for example, when a lengthwise end portion of the keycap is pressed, the keycap tilts or is bent to pivot circumferentially on a rubber actuator for pressing a switch part, which actuator is in contact with the center of the lower surface of the keycap.
As a reinforcement mechanism for compensating for such insufficiency of strength of the keycap, for example, Japanese Laid-Open Patent Application No. 2001-167657 proposes engaging a wire member with the lower surface of a keycap, where the wire member is formed by bending a metal wire of a stainless steel linear material of 1 mm in diameter so that the metal wire is sized to the shape of the keycap.
The wire member, which has an angular C-letter shape in plan view, includes a beam part extending in a lengthwise direction of the keycap and a pair of arm parts extending from both ends of the beam part at right angles with the beam part. The arm parts have their respective ends bent inward to form end parts of the wire member. The wire member is attached so that the end parts engage the holes or recesses of engagement parts projecting on the base of a membrane switch and the beam part engages the lower surface of the keycap. By thus causing the wire member to engage the lower surface of the keycap, the strength of the keycap is increased. As a result, the keycap moves downward in a horizontal position whichever part of its upper surface is pressed.
In the case of reinforcing a keycap on its lower surface side with a single wire member bent into an angular C-letter shape as described above, only one of the longer sides of the keycap, the one that engages the beam part of the wire member, is reinforced. Further, in the case where the keycap is molded to be thin to reduce its vertical dimension, the keycap itself is significantly reduced in rigidity. Accordingly, a pair of wire members is symmetrically placed to reinforce both of the longer sides of the keycap.
Reference may also be made to Japanese Laid-Open Patent Application No. 2008-251461 for related art.